docs: def reserve(self, table_name, key):
          """
          Reserve a job for computation.  When a job is reserved, the job table contains an entry for the
          job key, identified by its hash. When jobs are completed, the entry is removed.
          :param table_name: `database`.`table_name`
          :param key: the dict of the job's primary key
          :return: True if reserved job successfully. False = the jobs is already taken
          """
          job = dict(
              table_name=table_name,
              key_hash=key_hash(key),
              status='reserved',
              host=platform.node(),
              pid=os.getpid(),
              connection_id=self.connection.connection_id,
              key=key,
              user=self._user)
          try:
              self.insert1(job, ignore_extra_fields=True)
          except DuplicateError:
              return False
          return True